The present invention relates to a coated granular fertilizer comprising fertilizer particles the surface of which is coated with resins or inorganic materials, and, particularly, to a coated granular fertilizer coated with a film high in degradability in the natural environment.
Hitherto, the following techniques are known for obtaining fertilizers of slow activity.
The first is a technique to control release of fertilizer ingredients by chemical reaction having a specific reaction rate as represented by chemically slow active fertilizers such as CDU complex fertilizers and IB complex fertilizers.
The second is a technique to control release of the fertilizer from inside of the particles by coating the surface of fertilizer particles with a specific film.
Some films have hitherto been known. First, mention may be made of films mainly composed of sulfur. However, sulfur has the defect that it causes acidification of the soil and is considerably low in mechanical strength. Secondly, mention may be made of alkyd resins. However, alkyd resins are also low in mechanical strength, specially in shock resistance and abrasion resistance, and, as a result, a satisfactory slow action, namely, release controllability, cannot be obtained. Thirdly, mention may be made of urethane resins. Urethane resins are relatively high in mechanical strength, but they have problems in production and cost. Fourthly, mention may be made of polyolefin resins as disclosed in JP-B-60-37074. These resins are superior in mechanical strength and also in release properties, but are not necessarily satisfactory in degradability of the films in the natural environment after the release of fertilizer.
In addition to these techniques, various attempts have recently been made to provide coated fertilizers which do not leave films is the soil after release of fertilizer because the films undergo biodegradation or photodegradation in the natural environment and, furthermore, which can be satisfactorily controlled in release of fertilizer into soil. U.S. Pat. No. 3,295,950 discloses a technique according to which sulfur is used as a coating material and the surface of the coated fertilizer is further sealed by a wax. However, as mentioned in JP-A-55-167197, this technique has problems in that the film is fragile and can hardly control the release of fertilizer. Furthermore, the wax used for sealing is degraded by microorganisms relatively soon so as to cause a great change in develop- ment of the effect of the fertilizer depending on the soil conditions. Moreover, U.S. Pat. No. 3,372,019 and Canadian Patent No. 758,968 discloses coated fertilizers prepared using a molten mixture of a wax and an ethylene-vinyl acetate copolymer. However, these techniques are insufficient in the control of release properties. Additionally, inhibition of early release and control of release over a long time are difficult.
As techniques utilizing photodegradable films, techniques are known which use as a coating agent a vinyl resin containing an organometallic complex as disclosed in JP-B-7-91143, and techniques which use as a coating material a photodegradable copolymer such as ethylene-carbon monoxide copolymer or ethylene-vinyl acetate-carbon monoxide copolymer as disclosed in JP-B-2-23516, and techniques which use as a coating agent an amorphous polyolefin obtained by copolymerizing propylene, ethylene, and/or butene-1 as disclosed in JP-A-8-59382. These techniques, however, have a defect in that most of the films do not degrade in the soil which does not get light.
As techniques utilizing biodegradable films, JP-B-2-23517 discloses use of poly-3-hydroxy-3-alkylpropionic acid, JP-A-3-146492 discloses use of polycaprolactone, JP-A-7-315976 discloses use of aliphatic polyesters, and JP-A-7-33577 discloses use of polylactic acid. However, in these techniques, when the content of the biodegradable resins used, such as poly-3-hydroxy-3-alkylpropionic acid, polycaprolactone, aliphatic polyesters, and polylactic acid, is high, the releasing speed is too high due to the increase of hydrophilicity of the films. Additionally, degradation of the films occurs during the releasing period. Therefore, degradable film-coated granular fertilizers, the release of which is completed in a short period of time, can be obtained. But degradable film-coated granular fertilizers, the release of which is prolonged for a long period of time, cannot be obtained. On the other hand, when the content of the biodegradable resins is low, controllability of the release is good, but degradability of the film is insufficient. Furthermore, JP-A-7-33576 discloses a technique of coating, with a biodegradable resin such as polycaprolactone and a film material such as a low-molecular weight polyethylene or a wax, to form a multilayer film. However, the mechanical strength of the film is low, and inhibition of early release is insufficient.
As mentioned above, the conventional techniques do not simultaneously satisfy the controllability of release, the mechanical strength of the film, and the degradability of the film.
The object of the present invention is to provide a degradable film-coated granular fertilizer which is excellent in mechanical strength of the film, satisfactory in inhibition of early release and can be controlled in release for a long period of time, and whose film after the release of fertilizer is degraded in a natural environment, and to provide a method for producing the same.
As a result of intensive research conducted by the inventors, it has been found that the above problems can be solved by a coated granular fertilizer which is coated with a film containing a specific amount of a polyolefin and/or petroleum wax having a specific weight-average molecular weight and an inorganic filler and/or a surface active agent. Thus, the present invention has been accomplished.
The present invention is as follows.
(1) A coated granular fertilizer which comprises a degradable film containing 10% by weight or more of a polyolefin and/or petroleum wax having a weight-average molecular weight of 300-10,000 and an inorganic filler and/or a surface active agent and a granular fertilizer coated with said degradable film.
(2) A coated granular fertilizer according to the above (1) which is coated with a degradable film containing 10-95% by weight of a polyolefin and/or petroleum wax having a weight-average molecular weight of 300-10,000 and 5-80% by weight of an inorganic filler.
(3) A coated granular fertilizer according to the above (1) which is coated with a degradable film containing 10-99.99% by weight of a polyolefin and/or petroleum wax having a weight-average molecular weight of 300-10,000 and 0.01-20% by weight of a surface active agent.
(4) A coated granular fertilizer according to the above (1) which is coated with a degradable film containing 10-94.99% by weight of a polyolefin and/or petroleum wax having a weight-average molecular weight of 300-10,000, 5-80% by weight of an inorganic filler and 0.01-20% by weight of a surface active agent.
(5) A coated granular fertilizer according to the above (1) which is coated with a degradable film containing 10% by weight or more of a polyolefin and/or petroleum wax having a weight-average molecular weight of 300-10,000, an ethylene-vinyl acetate copolymer and/or an ethylene-xcex1-olefin copolymer having a weight-average molecular weight of 20,000 or more, a ratio of weight-average molecular weight to number-average molecular weight of 1-3 and a density of 0.8-0.9 g/cm3, and an inorganic filler and/or a surface active agent, the weight ratio of the ethylene-vinyl acetate copolymer and/or ethylene-xcex1-olefin copolymer to the polyolefin and/or petroleum wax being 0.01-2.0.
(6) A coated granular fertilizer according to the above (5) which is coated with a degradable film containing 10-94% by weight of a polyolefin and/or petroleum wax having a weight-average molecular weight of 300-10,000, 1-60% by weight of an ethylene-vinyl acetate copolymer and/or an ethylene-xcex1-olefin copolymer having a weight-average molecular weight of 20,000 or more, a ratio of weight-average molecular weight to number-average molecular weight of 1-3 and a density of 0.8-0.9 g/cm3, and 5-80% by weight of an inorganic filler.
(7) A coated granular fertilizer according to the above (5) which is coated with a degradable film containing 10-98.99% by weight of a polyolefin and/or petroleum wax having a weight-average molecular weight of 300-10,000, 1-60% by weight of an ethylene-vinyl acetate copolymer and/or an ethylene-xcex1-olefin copolymer having a weight-average molecular weight of 20,000 or more, a ratio of weight-average molecular weight to number-average molecular weight of 1-3 and a density of 0.8-0.9 g/cm3, and 0.01-20% by weight of a surface active agent.
(8) A coated granular fertilizer according to the above (5) which is coated with a degradable film containing 10-93.99% by weight of a polyolefin and/or petroleum wax having a weight-average molecular weight of 300-10,000, 1-60% by weight of an ethylene-vinyl acetate copolymer and/or an ethylene-xcex1-olefin copolymer having a weight-average molecular weight of 20,000 or more, a ratio of weight-average molecular weight to number-average molecular weight of 1-3 and a density of 0.8-0.9 g/cm3, 5-80% by weight of an inorganic filler, and 0.01-20% by weight of a surface active agent.
(9) A coated granular fertilizer according to the above (1) which is coated with a degradable film containing 10% by weight or more of a polyolefin having a weight-average molecular weight of 300-10,000 and an inorganic filler and/or a surface active agent.
(10) A coated granular fertilizer according to the above (9), wherein the polyolefin is a polyethylene.
(11) A coated granular fertilizer according to the above (5) which is coated with a degradable film containing 10-93.99% by weight of a polyethylene having a weight-average molecular weight of 630-10,000, 1-47.5% by weight of an ethylene-vinyl acetate copolymer, 5-80% by weight of an inorganic filler, and 0.01-20% by weight of a surface active agent, the weight ratio of the ethylene-vinyl acetate copolymer to the polyethylene being 0.05-1.0.
(12) A coated granular fertilizer according to the above (1), wherein the film contains 0.5-20% by weight of at least one biodegradable material selected from the group consisting of starch, modified starch, cereal powder, cellulose, agar, and xanthone.
(13) A coated granular fertilizer according to the above (1), wherein the film contains a photodegradation accelerator comprising an organometallic complex containing at least one metal selected from the group consisting of iron, cobalt, nickel, copper, manganese, silver, palladium, molybdenum, chromium, tungsten and cerium, and/or an oxidative degradation accelerator consisting of at least one member selected from the group consisting of a compound having a xe2x80x94Cxe2x95x90Cxe2x80x94 unsaturated bond, a transition metal and a transition metal compound.
(14) A coated granular fertilizer according to the above (13), wherein the organometallic complex is nickel dibutyldithiocarbamate and/or nickel diethyldithiocarbamate and/or an acetylacetone complex of iron, and the film contains the organometallic complex in an amount of 0.02-20xc3x9710xe2x88x926 mole/g based on the film.
(15) A method for producing the coated granular fertilizer according to any one of the above (1)-(14) which comprises a step of supplying a dispersion, solution or melt containing film-constituting ingredients in the form of spray to a granular fertilizer in a fluid or tumbled state to form a film on the surface of the granular fertilizer.
(16) A method for producing the coated granular fertilizer according to the above (15) which comprises a step of supplying a dispersion or solution containing the film constituting ingredients in the form of spray to a granular fertilizer in a fluid or tumbles state to form a film on the surface of the granular fertilizer.